Acute Megakaryoblastic Leukemia with t(1;22) Mimicking Neuroblastoma in an Infant

Myeloid sarcoma with RBM15::MRTFA (MKL1) mimicking vascular neoplasm

Extramedullary involvement of acute myeloid leukemia (AML), aka myeloid sarcoma, is a rare phenomenon in acute megakaryoblastic leukemia with RBM15:: MRTFA(MKL1) fusion, which might mimic non-hematologic malignancies. A 7-month-old infant presented with leukocytosis, hepatosplenomegaly, multiple lymphadenopathies, and a solid mass in the right thigh. Initially, the patient was diagnosed with a malignant vascular tumor regarding the expression of vascular markers from the biopsy of the right thigh lesion that was performed after the inconclusive bone marrow biopsy. The second bone marrow biopsy, which was performed due to the partial response to sarcoma treatment, showed hypercellular bone marrow with CD34 and CD61-positive spindle cell infiltration and > 20% basophilic blasts with cytoplasmic blebs. RNA sequencing of soft tissue biopsy revealed the presence of RBM15::MRTFA(MKL1) fusion. Based on these findings, myeloid sarcoma/AML with RBM15::MRTFA(MKL1) fusion diagnosis was made. AML with RBM15::MRTFA(MKL1) fusion can initially present as extramedullary lesions and might cause misdiagnosis of non-hematologic malignancies.

t(1;7;22)(p13;q21;q13) is a novel 3-way variant of t(1;22)(p13;q13) neonatal acute megakaryoblastic leukemia: A case report

Acute megakaryoblastic leukemia (AMKL) is a rare disease, occurring mostly in infants and young children. The chromosomal translocation t(1;22)(p13;q13), resulting in the RBM15-MKL1 fusion gene, is a recurrent and diagnostic translocation in infants with AMKL. The present case report describes a case of a newborn girl, without Down's syndrome, with congenital AMKL. At birth, the infant had hepatosplenomegaly and the peripheral blood count revealed anemia, thrombopenia and leukocytosis, with 28% blasts. Immunophenotyping demonstrated blasts positive for CD34, CD61 and CD42b. Karyotyping of these blasts (R-banding) showed a hitherto unreported chromosomal translocation, t(1;7;22)(p13;q21;q13), a 3-way variant of the t(1;22)(p13;q13) variant. Fluorescent in situ hybridization analysis confirmed the presence of the RBM15-MKL1 fusion gene.